Case Number: 17 -
33

Average reported concentration and consumption amount by one individual
that became ill

58.5

#/10 g

64

g

374

Highest average concentration reported in a packet of 6 bars

240

#/10 g

64

g

1540

Highest concentration reported in an individual bar

Exposed

Response

Attack rate

Comments

1

1

100%

Widespread outbreak geographically, with a large potentially
exposed and sick population, but details only available on one
individual

Comments

This was a nationwide outbreak attributed to chocolate bars
(16 g each) contaminated with S. Napoli. Although the overall attack rate
in the population exposed cannot be determined, details were given on three
individuals: a mother and two sons. All three ate two bars on the first day, and
one son ate two more bars on the second day. The son that ate chocolate bars on
both days became ill. He may have received a larger dose, or, alternatively, not
all the bars were contaminated and the ill child ingested a single contaminated
bar. We can only state that the attack rate for the one child that ate four
chocolate bars was 100%.

A box of chocolates, which consisted of 8 packets with 6 bars
in each packet, was obtained from a retailer from whom two patients had
purchased chocolate. This box of chocolates was analysed and 42 of the 48 bars
examined were positive, with the average concentration for the positive bars
reported to be 16 organisms per 10 g. The highest concentration for one bar was
240 organisms per 10 g, and the lowest was 3 organisms per 10 g. It was also
observed that the level of contamination per packet was not consistent. Packets
consisting of 6 bars that were all positive also tended to have a higher
contamination level. Of the 8 packets examined, the packet with the highest
average concentration was 58.5 organisms per 10 g.

Since information is only known about one case, these data
were not considered for further analysis.

Case Number:

18

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT4)

Setting:

Restaurant

Medium:

Roasted beef

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

2000

#/g

120

g

240 000

Reported concentration and consumption

Exposed

Response

Attack rate

Comments

5

3

60%

Reported exposed and positive numbers

Comments

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 135 000 (1500 CFU/g × 90 g) to 375 000 (2500 CFU/g × 150 g). Since
the size of the exposed population was reasonably small, it can be assumed that
the uncertainty associated with the exposed and positive populations is
minimal.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Min

Max

Value

Value

135 000

375 000

5

3

Case Number:

19

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis

Setting:

Caterer

Medium:

Grated yam diluted with soup

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

32 000

#/g

60

g

1 920 000

Reported concentration and consumption

Exposed

Response

Attack rate

Comments

123

113

91.87%

Reported exposed and positive numbers

Comments

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 1 080 000 (24 000 CFU/g × 45 g) to 3 000 000 (40 000 CFU/g × 15 g).
The exposed and positive populations in this case were potentially uncertain.
Since the degree of uncertainty is unknown, it was assumed that the reported
exposed population could not have been exceeded; however, there could have been
10% fewer people actually exposed. The number of positives reported was assumed
to represent the most likely number, but a 5% under- and over-reporting were
allowed for.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Pert distribution

Pert distribution

Min

Max

Min

ML

Max

Min

ML

Max

1 080 000

3 000 000

111

122

123

107

113

119

Case Number:

20

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT22)

Setting:

School lunch

Medium:

Beef and bean sprouts

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

40

#/g

22

g

880

Reported concentration and consumption

Exposed

Response

Attack rate

Comments

10 552

967

9.16%

Reported number of potentially exposed population

5 276

967

18.33%

Attack rate with 1/2 of the population exposed

3 517

967

27.50%

Attack rate with 1/3 of the population exposed

2 638

967

36.66%

Attack rate with 1/4 of the population exposed

Comments

The number of potentially exposed elementary school students
(6 to12 years old) was very large, since a central cooking facility served 15
schools. Patients were found from almost all the schools, but there was an
indication that most of the exposures occurred at 5 schools. It is highly
unlikely that all 10 775 people were exposed to contaminated food. As a result,
it was assumed that only a proportion, ranging from 1/2 to 1/4 of the total
potentially exposed population, were actually exposed. There could also be
uncertainty in the number of positives, but given the size of the denominator
(exposed population) and the size of the numerator (positives), incorporating a
5% allowance for under- and over-reporting has minimal effect on the attack rate
uncertainty range.

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 495 (30 CFU/g × 16.5 g) and 1375 (50 CFU/g × 27.5 g),
respectively.

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the values reported. The lower and upper bounds for the dose were estimated
to be 1 057 500 (35 250 CFU/g × 30 g) and 2 937 500 (58 750 CFU/g × 50
g). The exposed and positive populations in this case were also potentially
uncertain. Since the degree of uncertainty is unknown, it was assumed that the
reported exposed population could not have been exceeded, and also that there
could have been 10% fewer people actually exposed. The number of positives
reported was assumed to represent the most likely number, but 5% under- and
over-reporting was allowed for.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Pert distribution

Pert distribution

Min

Max

Min

ML

Max

Min

ML

Max

1 057 500

2 937 500

104

114

115

60

63

66

Case Number:

23

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis

Setting:

Confectionery

Medium:

Cake

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

6000

#/g

100

g

600 000

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

13

11

84.62%

Reported attack rate

Comments

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 337 500 (4500 CFU/g × 75 g) and 937 500 (7500 CFU/g × 125 g),
respectively. Since the size of the exposed population was reasonably small, it
can be assumed that the uncertainty associated with the exposed and positive
populations is minimal.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Min

Max

Value

Value

337 500

937 500

13

11

Case Number:

24

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT1)

Setting:

School lunch

Medium:

Peanut sauce

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

1.4

#/g

35

g

49

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

5320

644

12.11%

Reported attack rate

Comments

The attack rate that was reported for this outbreak was based
on exposure of the entire school population that received lunch from the central
kitchen. With such a large exposed population, which can be highly uncertain,
the estimated attack rate can vary widely. It is highly unlikely that the entire
reportedly exposed population was actually exposed to the contaminated food.
Unlike the prior school outbreak (Case Number 20), there was no indication in
this case of some schools being more likely to have been exposed than others. As
a result, it was assumed that only a proportion, ranging down to 1/2 of the
total potentially exposed population, were actually exposed. There could also be
uncertainty in the number of positives, but given the size of the denominator
(exposed population) and the size of the numerator (positives), incorporating a
5% allowance for under- and over-reporting has minimal effect on the attack rate
uncertainty range.

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 28 (1.05 CFU/g × 26.25 g) and 77 (1.75 CFU/g × 43.75 g),
respectively.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Pert Distribution

Min

Max

Min

ML

Max

Value

28

77

2660

3990

5320

644

Case Number:

25

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis

Setting:

Day care

Medium:

Cooked chicken and egg

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

27

#/g

150

g

4050

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

16

3

18.75%

Exposed and positive adults at day care

117

50

42.74%

Exposed and positive children at day care

133

53

39.85%

Exposed and positive population at day care

Comments

The food was a rice dish covered with cooked chicken and eggs.
Of 133 exposed people, 16 were adults (3 became ill) and 117 were children (50
became ill). Day care-aged children were assumed to be of increased potential
susceptibility to foodborne pathogens. Because of the outbreak setting (day
care), the exposed and positive populations were assumed to be well
characterized in this case.

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 2278 (20.25 CFU/g × 112.5 g) and 6328 (33.75 CFU/g × 187.5 g),
respectively.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Min

Max

Value

Value

2 278

6 328

16

3

2 278

6 328

117

50

2 278

6 328

133

53

Case Number:

26

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT1)

Setting:

School lunch

Medium:

Peanut sauce

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

<100

#/g

80

g

8000

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

2 267

418

18.44%

Reported exposed and positive population

Comments

The attack rate that was reported for this outbreak was based
on exposure of the entire school population that received lunch from the central
kitchen. With such a large exposed population, which can be highly uncertain,
the estimated attack rate can vary widely. It is highly unlikely that the entire
reportedly exposed population was actually exposed to the contaminated food. In
addition, the reported concentration per gram of food was less than 100 CFUs,
which introduces a second significant uncertain parameter.

Case Number:

27

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis

Setting:

Hospital

Medium:

Raw egg in natto

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

1.20E+06

#/g

50

g

6.00E+07

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

191?

45

23.56%

Reported exposed and positive population

Comments

Eggs were pooled in the preparation of this food. The number
exposed was the number of people who were served with this dish. Of the 191
served, 128 answered the food-intake questionnaire. Some of the hospital
patients could not talk. Among 128 responses, 36 did not actually consume this
dish. Among the 45 cases, 2 were tuberculosis (TB) patients and apparently had
taken antibiotics. The number of TB patients in the actual exposed population is
unknown. This outbreak is highly unusual because the dose is very high but the
attack rate is very low. In addition, the outbreak is reported to have occurred
in a hospital, an environment in which one might expect, depending on the
circumstances, the exposed population to be more susceptible than the overall
population. Because of the uncertainties in these data and the potential
confounding factors, this outbreak was not included for further
analysis.

Case Number:

28

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT4)

Setting:

Hospital

Medium:

Grated yam diluted with soup

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

2400

#/g

60

g

144 000

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

343?

75

21.87%

Comments

This outbreak is unusual, like the previous
hospital-associated outbreak (Number 27). Eggs were pooled and mixed well in
preparing this dish. The actual number of individuals exposed is suspected to be
lower than originally reported. The reported attack rate is lower than would be
expected at this high dose level. It should be noted that some of the patients
had antibiotic treatment, which may be a confounding factor in interpretation of
these data.

Case Number:

29

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT1)

Setting:

Hospital

Medium:

Tartar sauce

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

100

#/g

36

g

3600

Exposed

Response

Attack rate

Comments

126

36

28.57%

Comment

This outbreak is also unusual, similar to the previous two
hospital outbreaks, although in this case the dose is not as high as reported in
Numbers 27 and 28. Information about confounding factors in these hospital
outbreaks, such as diagnoses and treatments that patients were undergoing, was
not available. Therefore, the three Japanese hospital outbreaks were not
included in further analysis.

Case Number:

30

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis (PT1)

Setting:

Restaurant

Medium:

Cooked egg

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

200

#/g

30

g

6000

Reported concentration and attack rate and average amount consumed

Exposed

Response

Attack rate

Comments

885

558

63.05%

Comment

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the values reported. The lower and upper bounds for the dose were estimated
to be 3375 (150 CFU/g × 22.5 g) and 9375 (250 CFU/g × 37.5 g),
respectively. The exposed and positive populations in this case were also
potentially uncertain. Since the degree of uncertainty is unknown, it was
assumed that the reported exposed population could not have been exceeded, and
it was assumed that there could have been 10% fewer people actually exposed. The
number of positives reported was assumed to represent the most likely number,
but 5% under- and over-reporting was allowed for.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Pert distribution

Pert distribution

Min

Max

Min

ML

Max

Min

ML

Max

3 375

9 375

797

884

885

530

558

586

Case Number:

31

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

Salmonella Enteritidis (PT4)

Setting:

Confectionery

Medium:

Cake

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

14

#/g

30

g

420

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

5 103

1 371

26.87%

Comment

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the values reported. The lower and upper bounds for the dose were estimated
to be 236 (11 CFU/g × 22.5 g) and 656 (18 CFU/g × 37.5 g),
respectively. The exposed and positive populations in this case were also
potentially uncertain. Since the degree of uncertainty is unknown, it was
assumed that the reported exposed population could not have been exceeded, and
it was assumed that there could have been 10% fewer people actually exposed. The
number of positives reported was assumed to represent the most likely number,
but 5% under- and over-reporting was allowed for.

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Pert distribution

Pert distribution

Min

Max

Min

ML

Max

Min

ML

Max

236

656

4 593

5 102

5 103

1 302

1 371

1 440

Case Number:

32

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Enteritidis

Setting:

Day care

Medium:

Egg salad

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

0.78

#/g

30

g

23.4

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

156

42

26.92%

Comment

This outbreak was assumed to represent a susceptible
population since the outbreak occurred in a day care facility. In order to
incorporate uncertainty in the dose, the concentration and amount consumed were
assumed to have a potential range of 25% of the values reported. The lower and
upper bounds for the dose were estimated to be 13 (0.59 CFU/g × 22.5 g) and
37 (0.98 CFU/g × 37.5 g), respectively. The exposed and positive
populations were assumed to be well characterized in this case because of the
outbreak setting (day care).

Outbreak parameter uncertainty

Dose

Exposed population

Positive

Uniform distribution

Min

Max

Value

Value

13

37

156

42

Case Number:

33

Reference:

Ministry of Health and Welfare [Japan], 1999

Serovar:

S. Oranienburg

Setting:

Hotel

Medium:

Grated yam diluted with soup

Concentration

Amount ingested

Dose

Comments

Value

Units

Value

Units

5.00E+07

#/g

150

g

7.50E+09

Reported concentration and amount consumed

Exposed

Response

Attack rate

Comments

11

11

100.00%

Comment

In order to incorporate uncertainty in the dose, the
concentration and amount consumed were assumed to have a potential range of 25%
of the one reported. The lower and upper bounds for the dose were estimated to
be 4.22E+9 (3.75E+7 CFU/g × 112.5 g) and 1.17E+10 (6.25E+7 CFU/g ×
187.5 g), respectively. Since the size of the exposed population was reasonably
small, it can be assumed that the uncertainty associated with the exposed and
positive populations is minimal.